Until now greenhouses have traditionally been glass houses, that is, building frameworks of steel elements with glass mounted both on the sides and on the roof. The disadvantages of greenhouses of this type are that they are expensive to build, that it is too warm in them on sunny days, which requires temperature regulation measures, that their thermal insulation is very poor, which means that they require much heating in the winter, that they produce water condensation, that they do not lend themselves to large scale motorised working of the soil, etc. In recent years there are many cases where foldable greenhouse curtains have been mounted under saddle shaped greenhouse roofs. The greenhouse curtains can be used to regulate the amount of shadow and the temperature conditions and humidity to a certain extent.
Simple plant growing systems of the type described in U.S. Pat. No. 5,265,373 have been proposed which consist of pole constructions bound together on top by a framework which forms open horizontal or slightly sloping frame areas on which double foldable plant protection curtains are mounted so that the shadowing curtain can cover the whole frame area or leave it open. If frost protection is desired the shadowing curtain can be detached from the control cords and another curtain in the same frame area can be attached to them. If the shadowing curtain is perforated water cannot accumulate on it, but if the curtains are to serve as frost protection they must be waterproof. The problem is how to achieve water run off without formation of water pockets and how to support the weight of snow on a thin wire system. Solutions to these problems are not given in this document.
Through EP-A1-028 282 insulation for buildings in the form of halls, for example greenhouses, is known which consist of bubble films foldable in a zigzag pattern so that they can be used to insulate the inside of the glass roof or sides of the greenhouse as desired. The film is hung up via holders in wires and the opening width of the film folds can be regulated by changing the length of the spacers attached between the zigzag folds. Both in the bottom and in the upper part of the folds there are holes in the film for draining condensation water or for ventilating the multilayered film.
CA-A1-2,094,775 proposes a drainage system for retractable roofs in the form of membranes where wires have been drawn at even distances parallel to the roof ridges of the greenhouse to which the membranes lying on the roof trusses are attached with fasteners. This method of mounting the otherwise loose membranes means that they form a large number shell shaped depressions hung up at four points so that large amounts of water can accumulate, especially when the slope of the roof trusses is small.